Sharks are apex predators that structure marine communities through predation. Studies of diet and feeding patterns contribute to developing ecosystem models and it is critical that whenever possible, diet information specific to the area of concern is applied when developing an ecosystem model. Despite a number of studies conducted on tiger shark feeding, most comprehensive studies have been from the Pacific Ocean. There is little knowledge of the diet of tiger sharks in the Atlantic Ocean and Gulf of Mexico, with most studies in that area being localized and anecdotal. This study examines diet by life stage and tests for the presence of ontogenetic shifts, as well as how the diet of these sharks might be changing under certain environmental conditions and geographic variations. This study reviews the information collected on tiger shark feeding to date. It summarizes the results from previous studies on tiger shark diet: what prey items were found in studies of Pacific tiger sharks, and results from the anecdotal studies in the Atlantic, most of which took place in the early to mid 1900s, included small sample sizes, and were conducted in localized regions. For this study 169 sharks were caught as part of the U.S. shark bottom longline fishery and by the National Marine Fisheries Service Apex Predators scientific survey. Sharks were caught from North Carolina to Southern Florida and throughout the Gulf of Mexico and were divided, based on fork length, amongst three life-stage groups: young-of-the-year (YOY), juvenile, and adult. To quantify diet, index of relative importance was computed. Prey items were classified to the lowest taxon possible and sorted into 15 categories: aves, cephalopods, cnidarians, arthropods, elasmobranchs, bryozoan, mammals, molluscs, plants, reptiles, teleosts, porifera, other (rocks, trash), unknown, and free-living nematodes that were not tiger shark parasites. Overall, teleosts were the most significant prey category, followed by molluscs and birds. For YOY sharks, molluscs were the dominant category, followed by teleosts and birds. Juveniles primarily fed on teleosts, followed by molluscs and birds. Adults primarily consumed teleosts followed by reptiles and cephalopods. Cumulative prey curves were created for overall tiger sharks and each life stage to examine if sample size was large enough to describe the diet. Cumulative prey curves showed that the number of overall stomachs examined was enough to define the diet in the northwest Atlantic and Gulf of Mexico. However, although individual life stage curves approached asymptote, they did not fully reach one, indicating sample size was not necessarily sufficient for each individual life stage. Diet by life stage and region was also looked at using the Simplified Morisita-Horn Coefficient, as well as prey diversity using Simpson's Index. Dietary overlap was significant between all life stages except for YOY and adult. Prey diversity increased as sharks transitioned from one life stage to another. Effects of environmental factors (se...
Within the northern Gulf of Mexico, the Cuban Dogfish Squalus cubensis is the most frequently encountered squalid in continental shelf and slope waters. Despite the relatively high abundance of Cuban Dogfish in the region, there is a dearth of information regarding even the most basic aspects of the species’ biology. Furthermore, what has been reported is conflicting and of questionable utility. From 2005 to 2012, 139 male and 252 female Cuban Dogfish were collected opportunistically. The analyses indicated that male Cuban Dogfish reach 50% maturity at 379 mm stretch total length (STL) and are capable of reproducing throughout the year. Females reach 50% maturity at 466 mm STL and 50% maternity at 478 mm STL. Brood size ranges from one to four, and vitellogenesis and gestation are concurrent. Although samples were not collected during all months of the year, the presence of ova in the blastodisc stage of development during the summer and fall, coupled with the relatively high variability of embryo size within fall months, suggest that Cuban Dogfish reproduce asynchronously. Received October 29, 2012; accepted January 9, 2013
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